1. Field of the Invention
The present invention relates generally to systems and methods for transmitting and receiving digital signals, and in particular, to systems and methods for broadcasting and receiving digital signals using layered modulation techniques.
2. Description of the Related Art
Digital signal communication systems have been used in various fields, including digital TV signal transmission, either terrestrial or satellite.
As the various digital signal communication systems and services evolve, there is a burgeoning demand for increased data throughput and added services. However, it is more difficult to implement either improvement in old systems and new services when it is necessary to replace existing legacy hardware, such as transmitters and receivers. New systems and services are advantaged when they can utilize existing legacy hardware. In the realm of wireless communications, this principle is further highlighted by the limited availability of electromagnetic spectrum. Thus, it is not possible (or at least not practical) to merely transmit enhanced or additional data at a new frequency.
The conventional method of increasing spectral capacity is to move to a higher-order modulation, such as from quadrature phase shift keying (QPSK) to eight phase shift keying (8 PSK) or sixteen quadrature amplitude modulation (16 QAM). Unfortunately, QPSK receivers cannot demodulate conventional 8 PSK or 16 QAM signals. As a result, legacy customers with QPSK receivers must upgrade their receivers in order to continue to receive any signals transmitted with an 8 PSK or 16 QAM modulation.
Layered modulation techniques have been identified and developed to increase capacity, both in backwards compatible and non-backwards compatible implementations. Hierarchical modulation, particularly hierarchical 8 PSK (H-8 PSK), is also a special type of layer modulation that has been developed directed to a backwards compatible layered modulation implementation.
What is needed are systems and methods that improve layered modulation implementation, including hierarchical modulation implementations. Further, there is need for systems and methods that simulate the performance of layered modulation systems. The present invention satisfies these and other needs.